1. Field of the Invention
The present invention relates generally to impact expanding projectiles and, more particularly, to bullets with improved expansion characteristics which enable them to more closely resemble "ideal" hunting bullets.
There are several key features which are desired in bullets used for hunting big game or the like. They should have an aerodynamically efficient shape to produce true flight characteristics when fired. The ability to expand or flatten out upon impact with an objective is also highly desired to maximize tissue damage and shock. It is this latter characteristic which has been found to be the most difficult to perfect. The goal has been a controlled radial expansion with controlled deformation which is uniformly predictable notwithstanding typical variations in bullet impact speed and target composition or hardness. The complexity is further compounded by the need to maintain projectile integrity when engaging a target such that bullet disintegration or fragmentation is minimized or prevented during deformation. This has been especially difficult with respect to impact with relatively hard, boney material. Finally, the point of the projectile which commonly protrudes from the cartridge must be able to survive the rough handling associated with being carried and loaded into the firearm under the conditions of the hunt.
2. Description of the Prior Art
Methods for addressing the above objectives have resulted in an evolution of bullets which have a relatively hard covering or jacket partially or completely enclosing a soft core material in a variety of ways. One approach is the so called "mushrooming" bullet. In that design, the jacket does not completely encompass the nose of the core. The jacket is designed to collapse upon impact in a manner which causes the jacket to open radially at the nose, fold outwardly and peel back under the deforming exposed soft core material so that the bullet, in effect mushrooms upon impact. The nose usually is soft and may have a "hollow point" or an "insert", or other aids to initiating this outward radial expansion and mushrooming.
In an alternate approach, the nose itself is hard and does not deform. The jacket is weakened for a longitudinal span behind the nose. Upon impact the nose is pushed rearward and the projectile is caused to expand radially in an "accordian" fashion in the vicinity of the weakened portion of the jacket. The accordian type approach to collapsing deformation has provided some improvement in control of and reduced variation in radial expansion of the bullet, in response to variations in bullet speed and/or target composition and hardness in comparison to the mushroom approach. Also, this approach offers protection for the soft core material after impact and the bullet is thus less likely to disintegrate or lose as much of its mass on impact with typical targets. The tip of exposed soft core material associated with the mushroom approach often disintegrates or fragments upon impact and is more easily damaged or deformed during handling or loading which can seriously affect bullet aerodynamics.
Prior art designs which employ mushrooming type deformation are less desirable for most applications and generally inferior to the accordian expansion concepts, of which the present invention represents an improvement, and need not be addressed further. With respect to prior concepts in which the nose is not intended to mushroom, but expand in another manner, several prior art designs are believed to be of interest.
The first is found in U.S. Pat. No. 1,114,356 to Hoaglund. In Hoaglund the tip of the bullet is fully jacketed. The jacket is made in two parts, a nose portion and a body portion. The nose portion includes longitudinal grooves of a thinner section rearward of the nose itself which promote collapse upon impact. Upon impact, the nose section slides over the rear portion and expands "umbrella-like". Although this concept may serve certain applications, the unsupported rear of the resulting "umbrella" is also likely to collapse under stress. This impairs the ability of the bullet to retain and control sufficient radial expansion. In addition, a more conventional jacket of a single piece is less complex, and is easier and less costly to manufacture.
An early accordian concept employing a single piece jacket is found in U.S. Pat. No. 594,199 to Field. That design, however, lacks any additional means to facilitate nose collapse and expansion. Thus, deformation and expansion depend greatly upon target hardness. In cases of impact only with soft tissue or at slower speeds, the solid nose may well fail to collapse at all. It should be noted that the longated longitudinal holes around the projectile nose of Field are not `slits`, but rather `cutouts` which are milled or ground into the nose. Their thin, knife-like borders are stated to be for a different purpose, presumably for cutting. Such gaping holes, however, also distort the desired aerodynamically smooth profile and weaken the nose jacket, exposing more soft core material, and rendering the nose more likely to burst or fracture upon impact with harder, boney target material.
A third design, found in U.S. Pat. No. 1,715,783 to Rousseau, exhibits an enclosed nose having a central longitudinal hole in the front of the nose, but that bullet is devoid of slits in the jacket to aid or control expansion. The "cannelure" at the base of the nose does not weaken the nose enough to ensure proper expansion upon impact with targets of varying hardness. In fact, the inventor even states that no appreciable distension will occur when the bullet is fired into a solid target such as wood and bone. The bullet will, therefore, pass clearly through such a solid target. Such non-expansion characteristics are not desired in accordance with the present invention.
U.S. Pat. No. 1,155,901 to Duncan discloses a hard nose insert. However, Duncan provides no jacket slits nor other means of weakening the jacket to aid or to control radial expansion. Again, as in Rousseau, it appears that in many situations, no radial expansion would take place. Moreover, upon impact with harder targets, where sufficient force is encountered, the jacket very easily could burst and ramdon expansion or even disintegration ensue. Because the insert is not cylindrical, it would also, apparently, be very difficult to insert into the nose making the bullet more difficult and costly to manufacture.